Uplink scrambling during random access

ABSTRACT

The technology described in this case facilitates random access by a user terminal with a radio base station. A user terminal determines one of a first type of uplink scrambling sequences and generates a random access message using the determined one of the first type of uplink scrambling sequences. The random access message is transmitted to the base station. The user terminal receives from the base station a second, different type of uplink scrambling sequence and uses it for subsequent communication with the radio base station. For example, the first uplink scrambling sequences may be specifically associated with the radio base station&#39;s cell area or a random access radio channel associated with the radio base station, but they are not specifically assigned to any user terminal, and the second uplink scrambling sequence may be selected from a second set of uplink scrambling sequences specifically assignable to individual user terminals.

PRIORITY APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/835,782, filed Aug. 8, 2007, the entire contents of each of which arehereby incorporated by reference.

TECHNICAL FIELD

The technical field relates to mobile radio communications, and inparticular, to uplink communications involving mobile radio terminals ina mobile radio communications system.

BACKGROUND

Universal Mobile Telecommunications System (UMTS) is a 3rd Generation(3G) asynchronous mobile communication system operating in Wideband CodeDivision Multiple Access (WCDMA) based on European systems, GlobalSystem for Mobile communications (GSM) and General Packet Radio Services(GPRS). The Long Term Evolution (LTE) of UMTS is under development bythe 3rd Generation Partnership Project (3GPP) which standardized UMTS.There are many technical specifications hosted at the 3GPP websiterelating to Evolved Universal Terrestrial Radio Access (E-UTRA) andEvolved Universal Terrestrial Radio Access Network (E-UTRAN), e.g., 3GPPTS 36.300. The objective of the LTE work is to develop a framework forthe evolution of the 3GPP radio-access technology towards ahigh-data-rate, low-latency and packet-optimized radio-accesstechnology. In particular, LTE aims to support services provided fromthe packet switched (PS)-domain. A key goal of the 3GPP LTE technologyis to enable high-speed packet communications at or above about 100Mbps.

FIG. 1 illustrates an example of an LTE type mobile communicationssystem 10. An E-UTRAN 12 includes E-UTRAN NodeB (eNodeBs or eNBs) 18that provide E-UTRA user plane and control plane protocol terminationstowards the user equipment (UE) 20 over a radio interface. Although aneNB is a logical node, often but not necessarily implemented by aphysical base station, the term base station is used here to generallycover both logical and physical nodes. A UE is sometimes referred to asa mobile radio terminal and in an idle state monitors system informationbroadcast by eNBs within range to inform itself about “candidate” basestations in the service area. When a UE needs access to services from aradio access network, it sends a request over a random access channel(RACH) to a suitable eNB, typically an eNB with the most favorable radioconditions. The eNBs are interconnected with each other by means of anX2 interface. The eNBs are also connected by means of the S1 interfaceto an Evolved Packet Core (EPC) 14 which includes a Mobility ManagementEntity (MME) by an S1-MME and to a System Architecture Evolution (SAE)Gateway by an S1-U. The MME/SAE Gateway are referenced as a single node22 in this example. The S1 interface supports a many-to-many relationbetween MMEs/SAE Gateways and eNBs. The E-UTRAN 12 and EPC 14 togetherform a Public Land Mobile Network (PLMN). The MMEs/SAE Gateways 22 areconnected to directly or indirectly to the Internet 16 and to othernetworks.

In order to enable operation in different spectrum allocations, forexample to have a smooth migration from existing cellular systems to thenew high capacity high data rate system in existing radio spectrum,operation in a flexible bandwidth is necessary, e.g., bandwidths rangingfrom 1.25 MHz to 20 MHz for downlink transmissions from network to UE.Both high rate data services low rate services like voice must besupported, and because 3G LTE is designed for TCP/IP, VoIP will likelybe the service carrying speech.

LTE uplink transmission is based on so-called Discrete Fourier TransformSpread-OFDM (DFTS-OFDM) transmission, a low-peak to average power ratio(PAPR), single-carrier (SC) transmission scheme that allows for flexiblebandwidth assignment and orthogonal multiple access not only in the timedomain but also in the frequency domain. Thus, the LTE uplinktransmission scheme is also often referred to as Single-Carrier FDMA(SC-FDMA).

The LTE uplink transport-channel processing is outlined in FIG. 2. Atransport block of dynamic size is delivered from the media accesscontrol (MAC) layer. A cyclic redundancy code (CRC) to be used for errordetection at the base station receiver is calculated for the block andappended thereto. Uplink channel coding is then performed by a channelencoder which may use any suitable coding technique. In LTE, the codemay be a turbo code that includes a Quadratic Permutation Polynomial(QPP)-based internal interleaver for performing block interleaving aspart of the turbocoder. The LTE uplink hybrid-Automatic Repeat Request(ARQ) extracts, from the block of coded bits delivered by the channelcoder, the exact set of bits to be transmitted at eachtransmission/retransmission instant. A scrambler scrambles the codedbits on the LTE uplink (e.g., bit-level scrambling) in order torandomize the interference and thus ensure that the processing gainprovided by the channel code can be fully utilized.

To achieve this randomization of the interference, the uplink scramblingis mobile terminal-specific, i.e., different mobile terminals (UEs) usedifferent scrambling sequences. Terminal-specific scrambling alsoprovides the scheduler the freedom to schedule multiple users on thesame time-frequency resource and rely on base station receiverprocessing to separate the transmissions from the multiple users.Terminal-specific scrambling randomizes the interference from othermobile terminals in the same cell that happen to be scheduled on thesame resource and improves the performance.

After scrambling, the data is modulated to transform a block ofcoded/scrambled bits into a block of complex modulation symbols. The setof modulation schemes supported for the LTE uplink example include QPSK,16QAM, and 64QAM, corresponding to two, four, and six bits permodulation symbol, respectively. The block of modulation symbols is thenapplied to a DFTS-OFDM modulator, which also maps the signal to anassigned radio resource, e.g., a frequency sub-band.

Together with the modulated data symbols, the signal mapped to theassigned frequency band also contains demodulation reference signals.Reference signals known in advance by both the mobile terminal (UE) andthe base station (eNodeB) and are used by the receiver for channelestimation and demodulation of the data symbols. Different referencesignals can be assigned to a user terminal for similar reasonsterminal-specific scrambling codes may be used, i.e., to intelligentlyschedule multiple users on the same time-frequency resource and therebyrealize so-called multi-user MIMO. In case of multi-user MIMO, it is upto the eNodeB processing to separate the signals transmitted from thetwo (or more) UEs simultaneously scheduled on the same frequencyresource in the same cell. Terminals simultaneously scheduled on thesame frequency resource are typically assigned different (e.g.,orthogonal) reference signal sequences in order for the eNodeB toestimate the radio channels to each of those UEs.

A basic requirement for any cellular or other radio communicationssystem is providing a user terminal the capability to request aconnection setup. This capability is commonly known as random access andserves two main purposes in LTE, namely, establishment of uplinksynchronization with the base station timing and establishment of aunique user terminal identity, e.g., a cell radio network temporaryidentifier (C-RNTI) in LTE, known to both the network and the userterminal that is used in communications to distinguish the user'scommunication from other communications.

But during the (initial) random access procedure, uplink transmissionsfrom the user terminal cannot employ terminal-specific scramblingsequences or reference numbers to randomize interference because theinitial random access request message from the user terminal has juststarted communicating with the network and neither a terminal-specificscrambling code nor a terminal-specific reference number has beenassigned to that user terminal. What is needed is a mechanism thatpermits random access messages sent over a shared uplink channel to bescrambled until a terminal-specific scrambling code can be assigned tothe user terminal. One reason to scramble random access messages is torandomize inter-cell interference, which is also the case for scramblingduring “normal” uplink data transmission. Scrambling can also be used tosuppress intra-cell interference in case of multiple UEs being scheduledon the same time-frequency resource. Similarly, it would also bedesirable for user terminals to transmit known reference signals duringrandom access to allow the base station receiver to estimate the uplinkchannel. Reference signals need to be included in the random accessmessages as well as in “normal” uplink data transmissions to enablechannel estimation at the eNodeB and corresponding coherentdemodulation.

SUMMARY

The technology described below facilitates random access by a userterminal with a radio base station. A user terminal determines one of afirst type of uplink scrambling sequences and generates a random accessmessage using the determined one of the first type of uplink scramblingsequences. Its transmitter transmits the random access message to theradio base station. The user terminal receiver then receives from thebase station a second different type of uplink scrambling sequence. Theterminal uses that second different type of uplink scrambling sequencefor subsequent communication with the radio base station. In onenon-limiting example embodiment, the first type of uplink scramblingsequences may be specifically associated with the radio base station'scell area or a random access radio channel associated with the radiobase station, but they are not specifically assigned to any userterminal, and the second different type of uplink scrambling sequencemay be selected from a second set of uplink scrambling sequencesspecifically assignable to user terminals. Using these two differenttypes of scrambling sequences permits user terminals to scramble theiruplink signal transmissions even though terminal-specific scramblingcodes cannot be used in the uplink during random access by userterminals.

The user terminal transmits a first random access request messageincluding a random access preamble to the radio base station using arandom access channel radio resource. A second random access responsemessage is then received from the radio base station indicating a timingchange, an identified radio resource, and a temporary user terminalidentifier. The terminal adjusts a timing at the user terminal fortransmitting signals to the radio base station based on informationreceived in the random access response message, and based on theadjusted timing, transmits a third message corresponding to thegenerated random access message including the user's full terminalidentity to the radio base station over the identified radio resource.The third message is scrambled using the determined one of the firsttype of uplink scrambling sequence, modulated, and mapped to a radiochannel resource. The terminal receives a fourth contention resolutionmessage from the radio base station to complete the random accessprocedures and normal communications follow.

Various non-limiting embodiments map the first set of uplink scramblingsequences to some other parameter known by the user terminal and thebase station. For example, the first set of uplink scrambling sequencesmay be mapped to corresponding random access preamble sequences. One ofthe first set of uplink scrambling sequences may then be selected basedon the random access preamble included in the first random accessrequest message and the mapping. Another example maps the first set ofuplink scrambling sequences to corresponding user terminal identifiersand selects one of the first set of uplink scrambling sequences based onthe user terminal identifier included in the second random accessresponse message and the mapping. A third example maps the first set ofuplink scrambling sequences to corresponding radio resources used fortransmitting the random access request message and selects one of thefirst set of uplink scrambling sequences based on the random accesschannel radio resource used to send a first random access requestmessage including a random access preamble to the radio base station andthe mapping.

The two type scrambling sequence approach also may be used for referencesignals embedded in uplink random access messages sent to the basestation which are used by the base station to estimate the uplinkchannel, e.g., for equalization purposes, etc. One of a first set ofuplink reference sequences is selected, e.g., uplink reference sequencesspecifically associated with a radio base station's cell area or randomaccess channel but which are not specifically assigned to any userterminal. A random access message is generated using the selected one ofthe first set of uplink scrambling sequences and the selected one of thefirst set of uplink reference sequences. The user terminal transmits therandom access message to the radio base station. Thereafter, the basestation informs the user terminal of a second different type ofreference sequence to use in subsequent uplink communications, e.g., areference number assigned specifically to that user terminal.

In one non-limiting example implementation, the user terminal and basestation are configured to communicate with a long term evolution (LTE)radio communications network with the user terminal transmitting thefirst random access request message over a random access channel (RACH)and the third message over an uplink-shared channel (UL-SCH). The userterminal identifier sent by the base station in the second message maybe a temporary user terminal identifier used until a radio networkterminal identifier (RNTI) is assigned to the user terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 an example LTE mobile radio communications system;

FIG. 2 is a flow diagram illustrating non-limiting, example proceduresfor preparing a transport block delivered from the media access layer ofa user terminal for transmission over the radio interface to the networkin an LTE mobile radio communications system;

FIG. 3 is flow diagram illustrating non-limiting, example procedures fora user terminal to make a random access to the radio network;

FIG. 4 is flow diagram illustrating non-limiting, example procedures fora base station to receive and process a user terminal's random access tothe radio network;

FIGS. 5A and 5B illustrate a mapping between transport and physicalchannels in the downlink and uplink, respectively;

FIG. 6 is a diagram illustrating three basic states of a user terminal;

FIG. 7 is a signaling diagram illustrating a non-limiting example randomaccess procedure;

FIG. 8 illustrates a non-limiting example of a random access preambletransmission; and

FIG. 9 is a non-limiting, example function block diagram of a userterminal and an eNode B base station.

DETAILED DESCRIPTION

In the following description, for purposes of explanation andnon-limitation, specific details are set forth, such as particularnodes, functional entities, techniques, protocols, standards, etc. inorder to provide an understanding of the described technology. In otherinstances, detailed descriptions of well-known methods, devices,techniques, etc. are omitted so as not to obscure the description withunnecessary detail. Individual function blocks are shown in the figures.Those skilled in the art will appreciate that the functions of thoseblocks may be implemented using individual hardware circuits, usingsoftware programs and data in conjunction with a suitably programmedmicroprocessor or general purpose computer, using applications specificintegrated circuitry (ASIC), programmable logic arrays, and/or using oneor more digital signal processors (DSPs).

It will be apparent to one skilled in the art that other embodiments maybe practiced apart from the specific details disclosed below. Thetechnology is described in the context of an evolved 3GPP UMTS systemsuch as LTE in order to provide an example and non-limiting context forexplanation. See for example the LTE system diagram shown in FIG. 1. Butthis technology is not limited to LTE and may be used in any modernradio communications system. Moreover, the approach below which employstwo different types of scrambling sequences—one for purposes of randomaccess and one for communications after random access is completed—mayalso be applied to known channel estimation reference signals (sometimescalled pilot signals). However, the detailed explanation is providedusing scrambling sequences with the understanding that similar detailsapply to reference signals. For ease of description, a user equipment(UE) is often referred to without limitation as a user terminal or amobile terminal, and an eNodeB is referred to using the more general andfamiliar term base station.

FIG. 3 is flow diagram illustrating non-limiting, example procedures fora user terminal to make a random access to the radio network using anuplink scrambling code that is generally available to all user terminalsdesiring to randomly access service in a particular cell. The userterminal detects a first type of uplink scrambling sequences, e.g.,uplink scrambling sequences specifically associated with a radio basestation's cell area or random access channel but which are notspecifically assigned to any user terminal (step S1). A selected one ofthe first type of uplink scrambling sequences is determined (step S2),and a random access message is generated using the selected one of thefirst type of uplink scrambling sequences (step S3). The user terminaltransmits the random access message to the radio base station (step S4).After transmitting the random access message, the user terminal receivesfrom the radio base station a second, different type of uplinkscrambling sequence, e.g., an uplink scrambling sequence selected from asecond set of uplink scrambling sequences specifically assignable touser terminals (step S5). The user terminal uses the second type ofuplink scrambling sequence for subsequent communication with the radiobase station. Similar procedures can be used for known uplink referencesignals.

FIG. 4 is flow diagram illustrating non-limiting, example counterpartprocedures for a base station to receive and process a user terminal'srandom access to the radio network. Each base station in the network hasits own set of preamble sequences, reference signals, and non-terminalspecific scrambling codes or sequences. The base station broadcasts,implicitly or explicitly, over a broadcast channel, e.g., BCH, its setof preambles and uplink scrambling sequences (step S10). If the basestation does not explicitly broadcast the scrambling sequence to use,the identity of the cell from which the scrambling sequence to use maybe derived for example via a mapping between sequence and cellidentifier. The uplink scrambling sequences may be, for example,specifically associated with a radio base station's cell area or randomaccess channel and are not specifically assigned to any user terminal.The base station then waits to receive a first random access requestmessage from a user terminal that includes one of the base station'spreambles. In response, the base station transmits a second randomaccess response message to the one user terminal indicating a timingchange, an identified radio resource, and a user terminal identifier. Athird message corresponding to the generated random access message thatincludes the user terminal identity is descrambled using the selectedone of the first set of uplink scrambling sequences (step S11).Thereafter, the base station transmits to the user terminal a fourthmessage including a second different type of uplink scrambling sequenceselected from a second set of uplink scrambling sequences, e.g., uplinkscrambling sequences that are specifically assignable to user terminals(step S12). The user terminal uses the second uplink scrambling sequencefor subsequent communication with the radio base station. Similarprocedures can be applied for known uplink reference signals.

To better understand the following example and non-limiting LTE randomaccess procedure, reference is made to FIGS. 5A and 5B which illustratea mapping between transport and physical channels in the downlink anduplink, respectively. The following are downlink transport channels: thebroadcast channel (BCH), the paging channel (PCH), the downlink sharedchannel (DL-SCH), and the multi-cast channel (MCH). The BCH is mapped tothe Physical Broadcast Channel (PBCH), and the PCH and the DL-SCH aremapped to the Physical Downlink Shared Channel (PDSH). The uplinktransport channels include the random access channel (RACH) and theuplink shared channel (UL-SCH). The RACH maps to the Physical RandomAccess Channel (PRACH), and the UL-SCH maps to the Physical UplinkShared Channel (PUSCH).

In LTE, as in other mobile radio communication systems, a mobileterminal can be in several different operational states. FIG. 6illustrates those states for LTE. At power-up, the mobile terminalenters the LTE_DETACHED state. In this state, the mobile terminal is notknown to the network. Before any further communication can take placebetween the mobile terminal and the network, the mobile terminal needsto register with the network using the random access procedure to enterthe LTE_ACTIVE state. The LTE_DETACHED state is mainly a state used atpower-up. Once the mobile terminal registers with the network, it istypically in one of the other states: LTE_ACTIVE or LTE_IDLE.

LTE_ACTIVE is the state used when the mobile terminal is active withtransmitting and receiving data. In this state, the mobile terminal isconnected to a specific cell within the network. One or several InternetProtocol (IP) or other type data packet addresses have been assigned tothe mobile terminal, as well as an identity of the terminal, a CellRadio Network Temporary Identifier (C-RNTI), used for signaling purposesbetween the mobile terminal and the network. The LTE_ACTIVE stateincludes two substates, IN_SYNC and OUT_OF_SYNC, depending on whetherthe uplink is synchronized to the network or not. As long as the uplinkis in IN_SYNC, uplink transmissions of user data and lower layer controlsignaling are possible. If no uplink transmission has taken place withina given time window, the uplink is declared to be out-of-sync, in whichcase, the mobile terminal must perform a random access procedure torestore uplink synchronization.

LTE_IDLE is a low activity state in which the mobile terminal sleepsmost of the time in order to reduce battery consumption. Uplinksynchronization is not maintained, and hence, the only uplinktransmission activity that may take place is random access to move toLTE_ACTIVE. The mobile terminal keeps its IP address(es) and otherinternal information in order to rapidly move to LTE_ACTIVE whennecessary. The position of the mobile terminal is partially know to thenetwork such that the network knows at least the group of cells in whichpaging of the mobile terminal is to be done.

A non-limiting example random access procedure is illustrated in FIG. 7and includes four steps referred to as steps 1-4 with four associatedsignaling messages referred to as messages 1-4. The base stationtransmits a set of preambles associated with that base station, RACHresource information, and other information in a broadcast message sentregularly over a broadcast channel that active mobile terminalsregularly scan. In step one, after the user terminal receives anddecodes the information broadcast by the base station (eNodeB), selectsone of the base station's random access preambles and transmits it overthe RACH. The base station monitors the RACH and detects the preamblewhich allows the base station to estimate the transmission timing of theuser terminal. Uplink synchronization is necessary in order to permitthe terminal to transmit uplink data to the base station.

The random access preamble includes a known sequence, randomly selectedby the mobile terminal from a set of known preamble sequences availablefor random access purposes with a particular base station. Whenperforming a random access attempt, the terminal selects one preamblesequence at random from the set of preamble sequences allocated to thecell that the terminal is trying to access. As long as no other terminalis performing a random access attempt using the same preamble sequenceat the same time instant, no collisions will occur, and the randomaccess request will very likely be detected by the base station. Thepreamble is transmitted by a user terminal on a radio channel resource,e.g., a time/frequency resource, assigned for random access purposes,e.g., a RACH.

FIG. 8 illustrates conceptually a random access preamble transmissionaccording to the LTE specification as of this writing. One non-limitingexample for generating suitable preambles is based on Zadoff-Chu (ZC)sequences and cyclic shifted sequences thereof. Zadoff-Chu sequences mayalso be used, for example, to create the uplink reference signalsincluded in each data frame for channel estimation purposes.

A user terminal carrying out a random-access attempt has, prior to thetransmission of the preamble, obtained downlink synchronization from acell search procedure using timing information broadcast by the basestation. But as explained above, the uplink timing is not yetestablished. The start of an uplink transmission frame at the terminalis defined relative to the start of the downlink transmission frame atthe terminal. Due to the propagation delay between the base station andthe terminal, the uplink transmission will be delayed relative to thedownlink transmission timing at the base station. Because the distancebetween the base station and the terminal is not known, there is anuncertainty in the uplink timing corresponding to twice the distancebetween the base station and the terminal. To account for thisuncertainty and avoid interference with subsequent sub-frames not usedfor random access, a guard time is used.

Returning to the second random access signaling step shown in FIG. 7, inresponse to the detected random access attempt, the base stationtransmits a random access request response message 2 on thedownlink-shared channel (DL-SCH). Message 2 contains an index or otheridentifier of the random access preamble sequence the base stationdetected and for which the response is valid, an uplink timingcorrection or timing advance command calculated by the base stationafter processing the received random-access preamble, a scheduling grantindicating resources the user terminal shall use for the transmission ofthe message in the third message sent from the mobile terminal to thebase station, and a temporary user terminal identity used for furthercommunication between the user terminal and the base station. After step2 is completed, the user terminal is time synchronized.

If the base station detects multiple random access attempts (fromdifferent user terminals), then the random access request responsemessages 2 to multiple mobile terminals can be combined in a singletransmission. Therefore, the random access request response message 2 isscheduled on the DL-SCH and indicated on the Physical Downlink ControlChannel (PDCCH) using a common identity reserved for random accessresponse. The PDCCH is a control channel used to inform the terminal ifthere is data on the DL-SCH intended for that terminal and, if so, onwhich time-frequency resources to find the DL-SCH. All user terminalsthat transmitted a preamble monitor the PDCCH for a random accessresponse transmitted using the predefined common identity used by thebase station for all random access responses.

In the third step 3, the user terminal transmits the necessaryinformation in message 3 to the network using the scheduled uplinkresources assigned in the random access response message 2 andsynchronized in the uplink. Transmitting the uplink message in step 3 inthe same manner as “normal” scheduled uplink data, i.e., on the UL-SCH,instead of attaching it to the preamble in the first step, is beneficialfor several reasons. First, the amount of information transmitted inabsence of uplink synchronization should be minimized as the need forlarge guard time makes such transmissions relatively costly. Secondly,the use of a “normal” uplink transmission scheme for messagetransmission allows the grant size and modulation scheme to be adjustedto, for example, different radio conditions. Third, it allows for hybridARQ with soft combining for the uplink message which may be valuable,especially in coverage limited scenarios, as it allows relying on one orseveral retransmissions to collect sufficient energy for the uplinksignaling to ensure a sufficiently high probability of successfultransmission. The mobile terminal transmits its temporary mobileterminal identity, e.g., a temporary C-RNTI, in the third step to thenetwork using the UL-SCH. The exact content of this signaling depends onthe state of the terminal, e.g., whether it is previously known to thenetwork or not.

As long as the terminals which performed random access at the same timeuse different preamble sequences, no collision occurs. But there is acertain probability of contention where multiple terminals use the samerandom access preamble at the same time. In this case, multipleterminals react to the same downlink response message in step 2 and acollision occurs in step 3. Collision or contention resolution isperformed in step 4.

In step 4, a contention-resolution message is transmitted from the basestation to the terminal on the DL-SCH. This step resolves the contentionin case multiple terminals tried to access the system on the sameresource, by identifying which user terminal that was detected in thethird step. Multiple terminals performing simultaneous random accessattempts using the same preamble sequence in step 1 listen to the sameresponse message in the step 2, and therefore, have the same temporaryuser terminal identifier. So in step 4, each terminal receiving thedownlink message compares the user terminal identity in the message withthe user terminal identity they transmitted in the third step. Only auser terminal that observes a match between the identity received in thefourth step and the identity transmitted as part of the third stepdetermines the random access procedure as successful. If the terminal isnot yet assigned a C-RNTI, the temporary identity from the second stepis promoted to the C-RNTI; otherwise, the user terminal keeps itsalready-assigned C-RNTI. Terminals which do not find a match with theidentity received in the fourth step must restart the random accessprocedure from the first step.

As explained above, the user terminal identity included in message 3 isused as part of the contention resolution mechanism in the fourth step.Continuing in the LTE non-limiting example, if the user terminal is inthe LTE_ACTIVE state, i.e., is connected to a known cell and thereforehas a C-RNTI assigned, this C-RNTI is used as the terminal identity inthe uplink message. Otherwise, a core network terminal identifier isused, and the base station needs to involve the core network prior toresponding to the uplink message in step three.

In this non-limiting LTE example, only the first step uses physicallayer processing specifically designed for random access. The last threesteps use the same physical layer processing as for “normal” uplink anddownlink data transmission, which simplifies the implementation of boththe terminal and the base station. Because the transmission scheme usedfor data transmission is designed to ensure high spectral flexibilityand high capacity, it is desirable to benefit from these features alsowhen exchanging random access messages.

In the example non-limiting LTE context, the general processing stepsdescribed in FIG. 2 including CRC, coding, HARQ, scrambling, modulation,and DFT-S-OFDM modulation are applied by the user terminal to message 3in FIG. 7 and subsequent uplink transmissions from that user terminal tothe base station (there is no scrambling in the initial uplink randomaccess message in step 1). Different uplink scrambling sequences in theterminal depend on the type of uplink transmission. For the randomaccess message 3, a first type of scrambling sequence is used, e.g., acell-specific or random access channel-specific scrambling code. Forsubsequent “normal” data transmissions in the uplink, i.e., when thebase station has assigned a non-temporary identity to the terminal, asecond type of scrambling sequence is used, e.g., a terminal-specificscrambling code. A similar two-type approach may be used for uplinkreference signals used by the base station for channel estimation: afirst type, e.g., a cell- or random-access-specific reference signal forrandom access message 3, followed by a second type, e.g., a basestation-assigned or associated uplink reference signal sequence forfollowing “normal” data transmissions.

When the base station assigns a scrambling sequence and/or referencesequence to the mobile terminal, that terminal-specific scramblingsequence and/or reference sequence is(are) used for all subsequentuplink data transmissions for that particular uplink connection. Thescrambling sequence and/or reference sequence to be used can either beexplicitly configured in the mobile terminal or tied to the terminalidentity (e.g., a C-RNTI) that the base station assigns to a mobileterminal.

In the above, the user terminal uses a cell-specific scrambling sequenceto scramble message 3 because prior to performing random access, theuser terminal has decoded the base station's/cell's broadcastinformation and therefore knows the identity of the cell it isaccessing, the random access preambles associated with that cell, andcell-specific scrambling sequences and/or reference numbers. As long asmultiple terminals performing random access at the same time areassigned different time/frequency resources for their respective uplinkrandom access message 3, there is no interference between these usersand the lack of inter-user randomization is not a problem.

In a non-limiting embodiment, a one-to-one mapping is introduced betweenthe random access preamble sequence used in the random access requestmessage sent in step 1 of FIG. 7 and the scrambling sequence used forscrambling the random access message sent in step 3. Because both thebase station and the user terminal know the preamble used for the randomaccess request message sent in step 1 by the time message 3 is to betransmitted, both know which scrambling sequence to use.

In another non-limiting embodiment, the base station assigns thescrambling sequence for the user terminal to use for scrambling message3 as a part of the random access request response transmitted in step 2of FIG. 7, (i.e., before the transmission of message 3). As one example,this may be done by establishing a one-to-one mapping between thetemporary user identifier sent in message 2, e.g., a temporary C-RNTI,and the scrambling sequence to use.

Yet another non-limiting embodiment links the scrambling sequence to beused by the user terminal to scramble message 3 to the time-frequencyresource(s) used by the user terminal to transmit the random accesspreamble (message 1). In this case, the scrambling sequence will beknown to both the base station and the user terminal because both knowthe time-frequency resources used for the first random access requestmessage. For this embodiment, the scrambling sequence will be sharedbetween all user terminals transmitting a random access request preambleon the same time-frequency resource (s). But as long as all thoseterminals are assigned different time/frequency resources for their ownrandom access message 3, there is no interference between these usersand the lack of inter-user randomization is not a problem.

Combinations of one or more of the four different example embodimentsmay also be used. Again, the principles described in the abovescrambling sequence example and the four embodiments may also be used touplink reference numbers used for uplink channel estimation. In otherwords, one general or shared type of reference number may be used foruplink random access message 3, and another terminal specific typereference number may be used for subsequent uplink communicationsassociated with the connection.

There may be situations when the user terminal already has been assigneda identity but will still need to perform a random access. One exampleis when the terminal registers with the network, but losessynchronization in the uplink, and consequently, needs to perform arandom access attempt to regain uplink synchronization. Although theuser terminal has an identity assigned, terminal-specific scramblingcannot be used for message 3 in this case as the network does not knowwhy the terminal is performing the random access attempt until message 3is received. As a result, a cell-associated scrambling sequence ratherthan an outdated terminal-specific scrambling sequence needs to be used.

Accordingly, the benefits of terminal-specific scrambling for normaldata transmission are kept without impacting the functionality of therandom access procedure. As described above, terminal-specificscrambling randomizes interference which improves uplink transmissionperformance and provides additional flexibility in the schedulingdesign.

Although various embodiments have been shown and described in detail,the claims are not limited to any particular embodiment or example. Forexample, although primarily described in terms of scrambling sequences,the two type approach described for random access scrambling sequencesmay also be used for determining reference signal sequences sent in eachuplink frame which are used by the base station receiver for uplinkchannel estimation purposes. None of the above description should beread as implying that any particular element, step, range, or functionis essential such that it must be included in the claims scope. Thescope of patented subject matter is defined only by the claims. Theextent of legal protection is defined by the words recited in theallowed claims and their equivalents. All structural and functionalequivalents to the elements of the above-described preferred embodimentthat are known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe present claims. Moreover, it is not necessary for a device or methodto address each and every problem sought to be solved by the presentinvention, for it to be encompassed by the present claims. No claim isintended to invoke paragraph 6 of 35 USC §112 unless the words “meansfor” or “step for” are used. Furthermore, no embodiment, feature,component, or step in this specification is intended to be dedicated tothe public regardless of whether the embodiment, feature, component, orstep is recited in the claims.

1. A method implemented in a user terminal for accessing a radiochannel, the method comprises: transmitting a first message to a radiobase station, wherein the first message includes a random accesspreamble, and wherein the first message is transmitted using a randomaccess channel radio resource; receiving a second message from the radiobase station, wherein the second message indicates an identified radioresource and a user terminal identifier; selecting a first uplinkscrambling sequence based on the user terminal identifier included inthe second message; transmitting a third message to the radio basestation, wherein the third message includes a user terminal identity,the third message is transmitted over the identified radio resource, andthe third message is scrambled using the selected first uplinkscrambling sequence; and receiving a fourth message from the radio basestation, wherein the fourth message includes the user terminal identity.2. The method according to claim 1, further comprising: selecting asecond uplink scrambling sequence based on the user terminal identityreceived in the fourth message, and using the second uplink scramblingsequence for a subsequent uplink communication with the radio basestation.
 3. The method according to claim 12, wherein the first uplinkscrambling sequence is a cell-specific scrambling sequence correspondingto a cell associated with the radio base station.
 4. The methodaccording to claim 2, wherein the second uplink scrambling sequence is aterminal-specific scrambling sequence.
 5. The method according to claim1, wherein the user terminal communicates with a long term evolutionradio communications network, the first message is transmitted over arandom access channel, and the third message is transmitted over anuplink shared channel.
 6. The method according to claim 1, wherein theuser terminal identifier is a temporary user terminal identifier useduntil a radio network terminal identifier is assigned to the userterminal.
 7. The method according to claim 1, wherein the second messagefurther indicates a timing change, and wherein the method furthercomprises: adjusting a timing at the user terminal for transmittingsignals to the radio base station based on the timing change received inthe second message, wherein the third message is transmitted based onthe adjusted timing.
 8. A method implemented in a base stationassociated with a cell for responding to user terminals requestingservice from the base station over a radio channel, the methodcomprising: receiving a first message from a user terminal, wherein thefirst message includes a random access preamble and wherein the messageis received over a random access channel radio resource; transmitting asecond message to the user terminal, wherein the second messageindicates an identified radio resource and a user terminal identifier,and wherein the terminal identifier indicates a first uplink scramblingsequence; receiving over the identified radio resource a third messagefrom the user terminal including a user terminal identity, wherein thethird message is scrambled with the first uplink scrambling sequence;and transmitting a fourth message to the user terminal wherein thefourth message includes the user terminal identity.
 9. The methodaccording to claim 8, wherein the first uplink scrambling sequence is acell-specific scrambling sequence corresponding to a cell associatedwith the radio base station.
 10. The method according to claim 8,wherein the base station is part of a long term evolution radiocommunications network, the first message is received over a randomaccess channel, and the third message is received over an uplink sharedchannel.
 11. The method according to claim 8, wherein the user terminalidentifier is a temporary user terminal identifier used until a radionetwork terminal identifier is assigned to the user terminal.
 12. Themethod according to claim 8, wherein the second message furtherindicates a timing change.
 13. A user terminal for requesting servicefrom a base station having a cell area where the base station offersradio communications service, the user terminal comprising: a radiotransmitter configured to transmit a first message to a radio basestation, wherein the first message includes a random access preamble,and wherein the first message is transmitted using a random accesschannel radio resource; a radio receiver configured to receive a secondmessage from the radio base station, wherein the second messageindicates an identified radio resource and a user terminal identifier;electronic processing circuitry configured to select a first uplinkscrambling sequence based on the user terminal identifier included inthe second message; wherein the transmitter is configured to transmit athird message to the radio base station, wherein the third messageincludes a user terminal identity, the third message is transmitted overthe identified radio resource, and the third message is scrambled usingthe selected first uplink scrambling sequence; and wherein the receiveris configured to receive a fourth message from the radio base station,wherein the fourth message includes the user terminal identity.
 14. Theuser terminal in claim 13, wherein the electronic processing circuitryis configured to select a second uplink scrambling sequence based on theuser terminal identity received in the fourth message, and wherein thetransmitter is configured to use the second uplink scrambling sequencefor a subsequent uplink communication with the radio base station. 15.The user terminal in claim 13, wherein the first uplink scramblingsequence is a cell-specific scrambling sequence corresponding to a cellassociated with the radio base station.
 16. The user terminal in claim14, wherein the second uplink scrambling sequence is a terminal-specificscrambling sequence.
 17. The user terminal in claim 13, wherein the userterminal is configured to communicate with a long term evolution radiocommunications network, and wherein the transmitter is configured totransmit the first message over a random access channel and the thirdmessage over an uplink shared channel.
 18. The user terminal in claim13, wherein the user terminal identifier is a temporary user terminalidentifier used until a radio network terminal identifier is assigned tothe user terminal.
 19. The user terminal in claim 13, wherein the secondmessage further indicates a timing change, and wherein the electroniccircuitry is configured to adjust a timing at the user terminal fortransmitting signals to the radio base station based on the timingchange received in the second message, and wherein the transmitter isconfigured to transmit the third message based on the adjusted timing.20. A radio base station associated with a cell for responding to userterminals requesting service from the base station over a radio channel,comprising circuitry configured to: receive a first message from a userterminal over a random access channel radio resource, wherein the firstmessage includes a random access preamble; transmit a second message tothe user terminal, wherein the second message indicates an identifiedradio resource and a user terminal identifier, and wherein the terminalidentifier indicates a first uplink scrambling sequence; receive fromthe user terminal over the identified radio resource a third messagescrambled with the first uplink scrambling sequence, wherein the thirdmessage includes a user terminal identity; and transmit a fourth messageto the user terminal, wherein the fourth message includes the userterminal identity.
 21. The radio base station in claim 20, wherein thefirst uplink scrambling sequence is a cell-specific scrambling sequencecorresponding to a cell associated with the radio base station.
 22. Theradio base station in claim 20, wherein the base station is part of along term evolution radio communications network, the circuitry isconfigured to receive the first message over a random access channel andthe third message over an uplink shared channel.
 23. The radio basestation in claim 20, wherein the user terminal identifier is a temporaryuser terminal identifier used until a radio network terminal identifieris assigned to the user terminal.
 24. The radio base station in claim20, wherein the second message further indicates a timing change.